Investigation of precipitate in an austenitic ODS steel containing a carbon-rich process control agent

Austenitic oxide dispersion strengthened (ODS) steels are one of the candidates as a structural material for high-temperature applications in future power plants. To guarantee the necessary high production yield, the production process was improved in terms of reproducibility and scalability, by adding a process control agent (PCA) during the milling process. Due to this addition and the inherent change of the production process, the produced powder was thoroughly investigated using transmission electron microscopy and X-ray absorption spectroscopy methods to reveal the formation of chromium-rich carbides adjunct to titanium. Hence, less titanium was available to form the preferred complex nano-oxides the addition of carbon to the system influences the formation of precipitates severely in terms of their amount and size. The mechanical alloying process itself was unaffected by the addition of a PCA, and mixing and alloying of used elements still occurs. Keywords: Oxide dispersion strengthened steel, Mechanical alloying, Austenitic steel, Process control agent, Transmission electron microscopy, X-ray absorption spectroscop

Metastable Ta2N3 with highly tunable electrical conductivity via oxygen incorporation.

The binary Ta-N chemical system includes several compounds with notable prospects in microelectronics, solar energy harvesting, and catalysis. Among these, metallic TaN and semiconducting Ta3N5 have garnered significant interest, in part due to their synthetic accessibility. However, tantalum sesquinitride (Ta2N3) possesses an intermediate composition and largely unknown physical properties owing to its metastable nature. Herein, Ta2N3 is directly deposited by reactive magnetron sputtering and its optoelectronic properties are characterized. Combining these results with density functional theory provides insights into the critical role of oxygen in both synthesis and electronic structure. While the inclusion of oxygen in the process gas is critical to Ta2N3 formation, the resulting oxygen incorporation in structural vacancies drastically modifies the free electron concentration in the as-grown material, thus leading to a semiconducting character with a 1.9 eV bandgap. Reducing the oxygen impurity concentration via post-synthetic ammonia annealing increases the conductivity by seven orders of magnitude and yields the metallic characteristics of a degenerate semiconductor, consistent with theoretical predictions. Thus, this inverse oxygen doping approach - by which the carrier concentration is reduced by the oxygen impurity - offers a unique opportunity to tailor the optoelectronic properties of Ta2N3 for applications ranging from photochemical energy conversion to advanced photonics